The present invention relates to a novel antimicrobial aqueous dispersion or, more particularly, to an aqueous dispersion of fine particles of an antimicrobially effective compound hardly soluble in water as suspended in an aqueous medium containing a unique suspending agent.
It is a well established technology that various kinds of water-insoluble or hardly water-soluble solid compounds are employed in practical applications in the form of an aqueous suspension prepared by uniformly dispersing fine particles of the compound in an aqueous medium containing a so-called suspending agent having activity to stabilize the aqueous dispersion of the solid particles of the compound by preventing settling of the particles. The suspending agent currently under use is a water-soluble polymeric or water-dispersible compound exemplified by natural and synthetic polymers including gelatine, gum arabic, tragacanth, sodium alginate, bentonite, methylcelluose, salts of carboxymethyl cellulose, polyvinyl alcohol, salts of polyacrylic acid and the like. These suspending agents are used as selected depending on the particular solid material to be dispersed in the aqueous medium. In many cases, suspending agents are used in combination with a surface active agent as an emulsifying agent.
A problem in the use of these conventional suspending agents is that the suspending effect by the use of a suspending agent can be fully exhibited only by the use of a relatively large amount thereof requiring an amount of, for example, 2% by weight or even larger based on the total amount of the aqueous suspension. Therefore, a disadvantage is sometimes unavoidable in an aqueous suspension of a food or a medicament compound that the tastiness of the food or medicinal effectiveness of the medicament per se is adversely affected by the suspending agent so that the amount of the suspending agent must be decreased at the sacrifice of the suspending effect.
On the other hand, it is known that a biocellulose is produced when various kinds of acetic bacteria such as Acetobacter aceti, Acetobacter pasteurianus, Acetobacter aceti var. xylinam and the like are grown. The biocellulose obtained by this microbial method has a high purity as compared with conventional plant-origin celluloses and the degree of crystallinity, degree of polymerization and water-absorptivity can be easily controlled by selecting the culturing conditions of the bacteria so that biocelluloses are highlighted in recent years as a novel base material in various industrial fields.
Biocelluloses, however, are in general not free from problems and disadvantages. Since biocelluloses serve as a nutrient for the growth of certain bacteria and fungi, for example, they are susceptible to putrefaction or denaturation not to be storable for a long term at room temperature requiring refrigerating conditions for long-term storage in a refrigerator.
The above mentioned disadvantage of a biocellulose limits the industrial application fields of biocelluloses as a substitute for plant-origin celluloses and the only applications heretofore developed include the use thereof as an extender of paper products and as a filler in the paper sheets for loudspeaker cones and data cards.